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Revision as of 12:11, 19 February 2009 by Llib (talk | contribs) (spelling =P)
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What is a ramdisk?

A ramdisk is a portion of RAM utilised as a disk. Many distributions use /dev/ram for this, however Arch does not have a /dev/ram so we must use /etc/fstab to create ramdisks. The most important thing to remember about a ramdisk is that it is stored in RAM and thus volatile. Anything stored on a ramdisk will be lost if the computer completely sizes up, or loses power. Therefore, it is necessary to save the contents of your ramdisk to the harddrive if you want to save them.

Why use one?

As a ramdisk is stored in RAM, it is much faster than a conventional harddrive. So, if you need to manipulate files at high speed, a ramdisk could be the best solution. Possible uses are for /tmp, /var/cache/pacman, or /var/lib/pacman, although I'm sure you could think of many others.

How to create a ramdisk

To create a ramdisk, you must treat it as any other mounted filesystem. You must first pick and create a location for it to reside on, and then add it to your /etc/fstab file as follows:

none     /path/to/location     ramfs     0     0

If you don't have a lot of spare ram, it is recommended to use 'tmpfs' instead of 'ramfs', as tmpfs uses Swap when the available RAM starts to run out, whereas ramfs doesn't. of course, dipping into swap loses the performance benefits of RAM, so it's a little pointless unless you have a lot of spare RAM.

Example usage

Here is an example of the current (as of this writing) set up on my computer. I have edited /etc/fstab, /etc/rc.local, and /etc/rc.local.shutdown to store /tmp, /var/cache/pacman, and /var/lib/pacman in RAM, and sync them to disk before shutting down. I have removed portions of the files not relevant to the topic at hand to save space


none        /tmp         ramfs   defaults              0 0
none        /mnt/ramdisk ramfs   defaults              0 0


chmod 777 /tmp
touch /etc/ramdisk.sh

echo "#!/bin/dash" >> /etc/ramdisk.sh

echo "cd /var/ && tar cf abs.tar abs/" >> /etc/ramdisk.sh
echo "cd /var/cache/ && tar cf pacman.tar pacman/" >> /etc/ramdisk.sh
echo "cd /var/lib/ && tar cf pacman.tar pacman/" >> /etc/ramdisk.sh

echo "mkdir /mnt/ramdisk/var/" >> /etc/ramdisk.sh
echo "mkdir /mnt/ramdisk/var/cache/" >> /etc/ramdisk.sh
echo "mkdir /mnt/ramdisk/var/lib/" >> /etc/ramdisk.sh

echo "mv /var/abs /mnt/ramdisk/var" >> /etc/ramdisk.sh
echo "mv /var/cache/pacman /mnt/ramdisk/var/cache" >> /etc/ramdisk.sh
echo "mv /var/lib/pacman /mnt/ramdisk/var/lib" >> /etc/ramdisk.sh

echo "ln -s /mnt/ramdisk/var/abs /var/abs" >> /etc/ramdisk.sh
echo "ln -s /mnt/ramdisk/var/cache/pacman /var/cache/pacman" >> /etc/ramdisk.sh
echo "ln -s /mnt/ramdisk/var/lib/pacman /var/lib/pacman" >> /etc/ramdisk.sh
echo "ln -s /tmp /mnt/ramdisk/tmp" >> /etc/ramdisk.sh

echo "chmod 777 /mnt/ramdisk/tmp" >> /etc/ramdisk.sh
echo "rm /etc/ramdisk.sh" >> /etc/ramdisk.sh

chmod +x /etc/ramdisk.sh
/etc/ramdisk.sh &


echo "Saving contents of ramdisk to harddrive"
rm /var/abs
rm /var/cache/pacman
rm /var/lib/pacman
mv /mnt/ramdisk/var/abs /var
mv /mnt/ramdisk/var/cache/pacman /var/cache
mv /mnt/ramdisk/var/lib/pacman /var/lib